MILK-PLANT EQUIPMENT. 9 
7. Initial cost. 
8. Durability. 
9. Avoidance of chance of forcing the milk through at too high a speed. 
10. Ease and rapidity of operation. 
11. Elimination of milk pumps, whenever practicable. 
12. Adaptability to increased capacity, by installing additional units. 
13. Minimum of unnecessary agitation of milk. 
14. Floor space required. 
15. Minimizing human element in operation. 
16. Heating all of the milk uniformly. 
A pasteurizer with parts not easily accessible will require extra 
time to keep it clean and should be avoided. It is important that 
the pasteurizer have a large heating area, so that the temperature of 
the heating medium need not be much higher than the temperature 
to which the milk is to be heated. This will avoid the danger of 
heating some parts of the milk to too high a temperature, which 
gives it a scorched or burned taste and may also injure the cream line. 
To be on the safe side the temperature of the heating medium 
should not be more than 10° or 15° F. above that to which the milk 
is to be heated. As a heating medium water gives good results and 
its temperature should be under control at all times. Steam should 
not be used direct as a heating medium in most types of pasteurizers. 
By applying the so-called " regenerative " principle to the heating 
and cooling media many plants are able to cut down the amount of 
heat and refrigeration required. This principle may be applied by 
either the " milk regenerative " or the " water regenerative " system. 
With the milk regenerative system the cold milk coming into the 
pasteurizer passes through the first section of the cooling tubes over 
which the hot milk from the holder flows. In this way the incoming 
milk is partly heated, often to between 110° and 120° F. before it 
goes to the heater proper, while the milk going over the cooles is 
cooled by the incoming milk inside the tubes to 60° or 70° F. before 
it reaches the tubes containing the cooling water. 
With the water regenerative sj^stem the water from the first section 
of the cooler, having been heated to within a few degrees of the hot 
milk, needs to have only a few heat units added to it before it goes to 
the heater to heat the incoming milk. The water from the heater 
in turn having been cooled by the incoming milk goes to the cooler, 
where it is used for cooling the hot milk. The water regenerative 
system is the most desirable, as much cleaning of milk pipes is neces- 
sary with the milk regenerative system. Temperatures obtained with 
regenerative systems of pasteurizing are shown in Table 4. 
At many plants the milk is preheated by means of this regenerative 
principle to about 85° or 90° F. before it goes to the clarifier. At 
that temperature clarification is more efficient and less foam is pro- 
186608°— 20— Bull. 890 2 
